Optics for axially-transverse light emission

ABSTRACT

Apparatus, for illuminating a feature on a transparent light transmitting substrate or window, including an optical arrangement secured to one of the surfaces of the substrate for directing light into the substrate at an incident angle selected for propagation of light via total internal reflection (TIR) along the substrate. The optical arrangement has a rotationally symmetrical optic for surrounding a light source, a planar output surface, and an input surface divided into at least one curved zone bounded by a surface discontinuity, and at least one coupling material, with a refractive index greater than air, to optically and physically couple the output surface to the substrate.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.12/636,442, filed Dec. 11, 2009, incorporated herein by reference, whichclaims the benefit of U.S. Provisional Application No. 61/201,524, filedon Dec. 11, 2008, incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention concerns illuminating a transparent substance, such asexisting storefront window pane and particularly storefront panes. It isdesirable to illuminate in a cost-effective manner so as to attractattention and try to promote incremental sales.

Light (UV, visible and/or IR) from a source (e.g., LED, laser diode,optical fiber, fluorescent or photoluminescent materials) is opticallycoupled into a transparent substrate (e.g., storefront window) viatoroidal or circular (FIGS. 1, 1A, 1B, 2, 4, 12) prism couplers. Thesecouplers can be refractive (FIGS. 1, 1A, 1B), reflective (FIG. 4), orsome combination thereof, and comprise a refractive medium (e.g. oil,gel, water, adhesive, etc) between the optic (e.g. circular prism) andthe substrate (e.g. window) in order to non-invasively introduce lightinto the substrate at angles that cannot be introduced via air coupling.Use of such prism couplers to the face of a transparent substrate is oneelement of the invention disclosed herein. The light is then trappedwithin the substrate or window, which is akin to light trapped within anoptical fiber i.e., via total internal reflection, TIR. Definitions ofTIR, the ‘critical angle’ and the ‘evanescent wave’ appear in U.S. Pat.No. 5,959,777, column 2, line 56-Col. 3, line 8, and ‘optical contact’in Col. 1, lines 55-59 in the same patent, all incorporated byreference.

Light can then be extracted from the surface of the substrate or windowby defeating TIR via techniques known in the art. Examples of suchtechniques would be the application of scattering/fluorescing inks orthe lamination of surface or bulk diffusing films to portions of thewindow surface

2. Prior Art

Traditional edge lighting of a transparent substrate introduces lightinto the substrate along at least one edge thereof, and light is trappedin the substrate and propagates along the substrate as the light isreflected off the surfaces on the inside of the substrate (see, e.g.,U.S. Pat. No. 6,036,328).

FIG. 5 hereof illustrates a prior art transparent substrate or lightguide which is illuminated by edge lighting, particularly anuncollimated source (LED in this example) is coupled into the edge faceof a light guide, S1, separated by an air gap (n1=1.0).

FIG. 5 shows equations used in analysis of a traditional edge-lightingapproach for a light guide surrounded by air (n3˜1), receiving lightinto its entrance surface S1 from an air-coupled (n1˜1) LED having alambertian angular distribution. Note that FIG. 5 shows one planethrough the window. The light from the LED actually is emitted in ahemisphere comprising rays R1 that would be in and out of the plane ofthe illustrated flat panel light guide or pane, i.e., out of the pagehereof. In the analyses described herein, all calculations are for rayswithin the plane of the paper. One of skill in the art can determine theeffects at other angles out of the plane of the paper.

FIG. 6 illustrates analysis results for a light guide of FIG. 5 having arefractive index, n2, of 1.51. Note that the light rays (for all angles)reflect off the sidewall surfaces S2 and S4 via total internalreflection (TIR). However, all angles also exit surface S3, oppositeentrance surface S1. Note also that the incident angles (relative toaxis AX2) at surface S2, identified as (90−θ2) are restricted to anglesbetween 48.53 and 90 degrees. Further, the critical angle at surface S2,(90−θ2)=a sin(n3/n2)=41.47 degrees, and its complement is(90−41.47)=48.53 degrees. Therefore, for the geometry shown in FIG. 5,it is physically impossible for rays to strike surface S2, relative toaxis AX2, between the critical angle and its complement.

Since the rays from the LED, R1, span the entire gamut of ray angles,−90°≦θ1≦90° into S1 (see column 2 in FIG. 6; only positive angles areshown), one can see that for a rectangular slab light guide (i.e., amall window), light introduced at one end face, S1, will leak out theother end face, S3, unless a reflective material is affixed on oradjacent to S3.

An alternate edge lighting approach would be to optically couple the LEDto the edge face, S1, instead of using an air gap. That would introduceall angles within the light guide, and so rays R2 would extend−90°≦θ2≦90°, and so light within a range of angles would leak out ofedge faces S2 and S4. For example, for n2=1.51, rays R2 would leak outof face S2 for θ2>48.53°; i.e. the incident angle at S2 relative to axisAX2, (90−θ2) the critical angle, or 41.47°). So, to prevent leakage,reflective tape would then be placed on portions of S2 and S4 startingat point intersecting with face S1, wherein the length of the tapeprogressively gets longer as the LED moves along edge S1 further awayfrom the intersection with S2 and S4, respectively.

One then might consider partially collimating the LED before opticallycoupling to the edge face, S1. First, a typical lens would lose itsability to collimate if its curved output face were optically coupled tothe edge face S1 (unless the refractive index of the lens was very highin order to maintain the appropriate Δn). A non-imaging approach mightwork, with the exit face optically coupled to the edge face, S1, and thecollimation set θ2<48.53°, which would preclude leakage out of face S2,although not out of S3 unless the incident angle at S3 relative to axisAX7, θ2, is greater than the critical angle or 41.47°. Note that sinceS2 and S3 are planar surfaces at the angle of incidence, the anglesdiscussed above work the same when reflected about the axis beingconsidered (these can be considered as negative angles). Further, forthe ordinary case of a rectangular slab (window), there is arelationship between the critical angle at S2 and that at S3. Forexample, at S2, there will be TIR for angles (90−θ2)>41.47°, which canbe rewritten (90−41.47°)>θ2, and thus θ2<48.53°. At S3, TIR will occurif θ2>41.47°. Therefore, combining both constraints, TIR can occur atboth S2 and S3 if 41.47°<θ2<48.53°; i.e. for θ2 between the criticalangle at S2 and its complement. However, as stated previously, thisrange of angles is not possible for that shown in FIG. 5. Finally, notethat non-imaging optics (when used with a multi-lumen LED) would have alength that may interfere with existing structures in retrofitapplications, and might require additional spacing between adjacent mallglass windows in new installations (or require wider window frames for agiven size exterior window). The length of the optic would scale withsmaller LEDs (see general discussion of non-imaging optics in U.S. Pat.No. 5,971,551 noting that a collimator is but a concentrator inreverse), but then many more LEDs would be required to achieve the samenumber of lumens, all else being equal.

Second, the natural compression of angles once inside the light guide,in the edge lighted air-gap approach, −41.47°≦θ2≦41.47° (for n2=1.51,typical for glass) limits the spread of light through from the point ofentry at face S1 (see e.g., FIG. 17F). Compare this with theomnidirectional spread of the instant invention shown in FIG. 17B.Therefore, for the edge lighted air gap approach, in order to fill thewindow with light, one would need a substantial number of LEDs alongedge face S1. Further, since the span across the window can be ratherlarge (say 4-6 feet for mall glass), then due to losses (absorption,scatter, etc) over that span, one would need to fill the opposing edgeface, S3 with LEDs as well in order to provided reasonably uniform lightacross the window (see e.g., FIG. 17I).

By use of the prism coupling approach hereof, light can be injected atprecisely the location(s) on the window where it is needed since it isnot restricted to a location at the edges of the window.

Light in the window or light guide may be caused to escape the lightguide, rather than being internally reflected. The escape may be causedby some treatment at selected locations on a surface of the light guide.Typical ways used to cause escape may include a film applied to asurface at selected locations, e.g., described in U.S. 2007/0279554 andU.S. Pat. No. 6,171,681, e.g., cling film and electret film, describedin U.S. 2004/0043221 (the '221, referenced below). See U.S. Pat. No.5,319,491, col. 2, line 40-col. 3, line 26, incorporated by reference,which describes additional approaches for coupling light out of asubstrate.

For example, indicia on a cling film may be caused to glow, e.g., by afluorescent substance applied to them when the film is directly mountedto the light guide and the indicia are illuminated by a light sourceoptically coupled to an appropriate optic. Optical coupling occursbetween the light guide and the cling film, even without need for aninterposed coupling medium between them.

DESCRIPTION OF THE EMBODIMENTS

The following is a description of some embodiments. It is not intendedto limit the scope hereof, as other embodiments and arrangements mayalso achieve the same objective and operate and perform in a similarmanner.

As shown in FIGS. 1 and 7, a side-emitting light emitting diode (seee.g., U.S. Pat. No. 6,598,998, filed May 2001, and commerciallyavailable e.g., Lumileds P/N LXHL-DW03) is fitted with a special opticwhich is in the general shape of a thick countersunk flat washer madefrom clear acrylic or polycarbonate. That assembly is affixed to theface (not to an edge) of a window pane, e.g., via double stick tape suchas 3M Scotch brand clear mounting tape, P/N 4010T. This arrangement,which is known as ‘prism-coupling’, (see, e.g., U.S. Pat. No. 4,545,642)forces light to travel within the window pane as if it were a lightguide. Light is thereby trapped within the window pane via totalinternal reflection. This allows light to be coupled into the face ofstorefront window (or other transparent substrate), causing the windowto act like a light guide and enabling it to perform many of theapplications known to use such guides. In the inventor's opinion, thearrangement allows easy coupling to existing, installed windows, whereastraditional edge lighting techniques would require access to the edgesof the window, which in many instances would be a costly endeavor. Oneof skill in the art of light guides would normally have employed edgecoupling, not prism coupling; see, e.g., U.S. Pat. No. 6,036,328(traditional edge lit) and U.S. Pat. No. 6,679,621 (LED withside-emitting lens into clearance holes within a substrate).

LEDs are available from a number of suppliers, including Lumileds, Cree,Seoul Semiconductor, Osram, Nichia, etc. Some of these manufacture LEDsin the UV and violet wavelengths; e.g., Cree UV LEDs, P/NXR7090UVV-L100-0001. The advantage of using UV is that it can excite alarger number of fluorescent colors than could a blue LED (because UVwavelengths are shorter). There are safety concerns when using UV LEDsre: damage to the human eye/skin. The data shows that wavelengthsgreater than 320 nm are desirable from a safety perspective. Bycarefully considering the excitation spectra of the fluorescent materialbefore selecting the LED wavelength, one can minimize the safety risk bychoosing LEDs with longer wavelengths. Of course other factors need tobe considered, such as efficacy, cost, supplier availability, etc, inorder to achieve the appropriate balance of safety margin, price andperformance.

The LED surface temperature will present a thermal shock to the windowand so the coupling method between the LED and the window shouldintroduce a sufficient thermal break to avoid window damage. One suchmethod may be the use of a thick layer of high temperature couplinggrease, keeping in mind any modified ray distributions from the LED whenpassing through the grease, such as that due to bubbles in the greaseand the expanded area of the grease compared to the LED. Another may beto interpose a layer of shock-resistant glass (e.g., borosilicate) whoseoptical properties are consistent with the application (e.g., wavelengthtransmittance, low haze, etc.). In both instances, the heat from the LEDis preferentially conducted away from the window (to a thermally bondedheatsink), thereby lowering the surface temperature of the LED andminimizing the thermal shock to the window, especially important whenthe window has thermally stabilized at a low temperature (e.g.,uninsulated window pane during a cold winter day) where a thermal shock(from the concentrated heat load of the LED) might cause the window tocrack.

Light can be extracted from any point or area or the window by applyingto the window something that scatters light that impinges on it. Forexample, as shown in FIG. 13, one may write on the window with afluorescent marker (see extraction feature EF1), such as those used withilluminated menu boards in restaurants (e.g., P/N WO2000MKR4 fromInternational Patterns) or affix a window film (see WF1) withcomputer-printed graphics (with the appropriate light scattering ink ordiffusing feature, EF2, such as matte finished Scotch™ tape) or simplyabrading the surface (EF4), or even procure windows that have scatteringfeatures embedded therein (EF3). The Detailed Description hereof showsother techniques. Some other known techniques are described in theBackground section hereof.

In addition to windows, it is contemplated that the invention can beused with signboards, tabletops, mailboxes, glass doors, toys, etc.,that is any object which acts as a light guide. A table is set forthbelow indicating standard rural mailbox dimensions for various sizes andseries of rural mailboxes, the letters representing the dimensionscorresponding to the letters appearing in FIG. 20B-1.

A B C D E E11 Series Standard (T1) Size 8.75 6.75 19.00 5.38 10.60 inE16 Series Large (T2) Size 10.88 8.50 20.25 6.63 13.35 in ST20 SeriesJumbo (T3) Size 15.00 11.50 23.50 9.25 18.06 in Standard (T1) Size222.25 171.45 482.60 136.53 269.31 mm Large (T2) Size 276.23 215.90514.35 168.28 339.13 mm Jumbo (T3) Size 381.00 292.10 596.90 234.95458.83 mmFIG. 20B-2, which shows a flattened view of a T2 size mailbox, indicatesthat the mailbox shown includes two 4.25″×20.25″ seasonal/personalizeddecal areas 72, two PT15-150 flexible solar cells connected in parallel74, a window decal 76, a laminated extraction film 78, a reflector film80, and an LED/prism 82. The window decal can be non-coupling (e.g.,cling-type or low index coupled). The window decal can also be coupled(e.g., back-side water coupled with front-side scattering ink, orback-side coupled via selectively placed adhesive dots with front-sidescattering ink). Both the laminated extraction film and the reflectorfilm can optionally be provided with a coupled decal. It should be notedthat the front-side scattering ink can also work in sunlight; the inkcan be a combination of white, fluorescent, and colored materials. Arealdensity of the ink and/or the coupling materials can be distributed toensure uniform illumination, (both in sunlight and when the LED isilluminated). Any suitable ray trace program, such as Lighttools fromOptical Research Associates, can assist in the design. Such computerassisted designs can provide a marketing edge in the sale of decals. Itshould also be noted that the curvature of the mailbox will cause raysfrom the LED/prism to alter their angular properties, and, thus, shouldbe considered in an overall design of the optical approach (refractiveindices, prism dimensions, LED collimations, etc.) which can beoptimized by any suitable ray trace program. The LEDs can be integratedwithin the glass clamps that support the window or signboard (e.g., fromCR Laurence and NovaDisplay, respectively), or some other feature (e.g.,the support for a rural mailbox flag). Alternatively, they can besupported by a window decal (similar to the half-baseballs in the fakebroken-window decals, and optically coupled using e.g., water). Windowdecals can also be laminated.

Some or all of the extraction features can also scatter light and/orglow in response to external light sources such as the sun, a spotlight,etc such that the LEDs might be used only at night, or might beilluminated continuously and/or pulsed as an accent.

Different wavelength LEDs may be used (UV, visible, IR) and theirintensity may can be varied to attract attention within a single window,or may be coordinated between an array of windows e.g., mall storefrontsor the facade of a high-rise or be otherwise disposed on the window(s).

The LEDs can be flashed on-and-off in order to act, in part or in full,as a communication medium via extraction patterns on the window. Forexample, in a mall-setting, one store's window can communicate withanother's, thereby providing wireless links to coordinate specialeffects, further enhancing the retrofit opportunities. As is well knownin the art, the LEDs can be flashed at high frequencies unperceivable bythe human eye.

As more extracting features are placed across a window, more LEDscoupled at one location to the surface of the substrate or coupled atseveral locations across the substrate surface may be necessary tomaintain a consistent brightness level, all other things being equal.

In order for the light from the LED to travel across the span of thewindow, the window material must be very clear and have high lighttransmission. Altuglas International's Plexiglas MC, an acrylic sheet,rated highest for visible light transmission (T_(vis)) among availablewindows (glazing), followed by low-iron glasses such as PPG's Starphireand Pilkington's Optiwhite. For optimal transmittance of UV light in aplastic sheet, Spartech's Solacryl SUVT is suitable. In addition totransmittance, other properties must be carefully considered, such ashaze, surface finish, impact resistance, and cost. For example, amailbox was fabricated (by California Quality Plastics Inc.) from a highimpact resistant plastic (Acrylite Plus), but the transmittance waslower than one fabricated from Acrylite GP.

Commercially available acrylic sheets (e.g., CYRO Industries' ACRYLITEEndLighten, Altuglas' Elit II, and Lucite International's PerspexPrismex) that are designed to be edge-lighted from a fluorescent lamp,and are known to already have small extraction features preciselydistributed across their surface(s) (e.g., via an array of printed dotson their surface; see, e.g., U.S. Pat. No. 4,937,709, filed August 1989)provide uniform illumination. Such a dot pattern may be optimized foruse with the instant invention. In fact, there are large-bed inkjetprinters that can dispense white ink and it is contemplated that othermaterials (e.g., micron-sized glass beads and/or fluorescent inks in aUV curable adhesive that matches the refractive index of the window) canbe dispensed, silk-screened, etc., and that would cause light to exitthe window in a predetermined pattern.

The LEDs require a suitable source of electrical power as is known inthe art and these range from simple (continuous DC current) tosophisticated (computer-controls for arrays of LEDs).

The LED power source may be located a distance from the LED. It has beenfound that microphone cable (manufactured by Mogami) provides excellentflexibility and can handle the typical current (e.g., 700 mA) of astring of high brightness LEDs. Should the LED be placed towards thecenter of a window, it may be desirable to use very thin wires (LEDstypically require 700 milliamps or less) or transparent conductors(e.g., vacuum deposited layer of Indium Tin Oxide (ITO) on opticallyclear film) to carry the current to the LED without being obtrusive.

High brightness LEDs typically consume between 1 and 5 watts, and due totheir small size require heat sinking. Suitable heatsinks andthermal-grade adhesives & greases can be found from hobbyist partsdistributors. One suitable heatsink used was P/N G15275. These heatsinkscan also be anodized in different colors and patterns. The LED's anodeand cathode leads can be electrically isolated from the heatsink viapolyimide tape.

Another approach to thermal management is to use the heatsinkingcapacity of the end-device. For example, the LED can be thermally bondedto the inside of the glass clamps previously mentioned. CR Laurence P/NZ412BN is cast zinc, and its thermal efficiency vs. aluminum isdiscussed in “Efficiency and Cost Tradeoffs between Aluminum andZinc-Aluminum Die Cast Heatsinks”. LEDs have also been thermally bondedto aluminum L-shaped extrusions (available from Home Depot) andfabricated into the shape similar to the abovementioned glass clamp.Another embodiment used the twisted (and flexible) aluminum shafts usedto support the ‘lollipop’ style driveway markers (also available fromHome Depot). The LED was thermally bonded to one end of the shaft, andthe other end was hung from a suction cup attached to a window. It iscontemplated that the shaft can be bent into decorative shapes while theheat is transferred along the length of the shaft and dissipated intothe air (the shaft advantageously has a cross-shaped cross-section,adding additional surface area thereby enhancing heat dissipation). Heatpipes can also be used.

The optic is placed around the side emitting LED and directs the lightinto the substrate. As previously mentioned, the initial embodiment wasformed in the shape of a thick flat washer with a countersunk interiorhole, but made from clear acrylic and polycarbonate (see FIG. 1).Additional embodiments are shown in FIGS. 2 and 4.

Various types of coupling media for filling any gap between the opticthat delivers light to the substrate and the substrate have beensuccessfully utilized, including tap water, hair-gel, food-grade grease,Vaseline petroleum jelly, double-stick tape, acrylic based sealant,mineral oil and microscope coupling fluid. Some coupling media, like 3MScotch-brand double stick tape, can also support the weight of theLED/heatsink assembly. Greases and sealants are especially useful whenused with glass clamps as they do not run-off like mineral oil and tapwater. The key aspects of this media are its refractive index and itsclarity. The index must be high enough so that light can exit the opticand enter the window at the appropriate angles. High clarity ensureshigh coupling efficiency. Note that other properties of the media alsoshould be considered, such as thickness (vis-à-vis clarity and itseffect on the path of light rays), thermal insulation, compliance toaccommodate mismatches between the coefficient of thermal expansionbetween the optic and the window or substrate, adhesion overenvironmental conditions, ease of removal during servicing orrepositioning, and stability under prolonged exposure from ultravioletlight (either from the LED or sunlight). Further, the overall designapproach should avoid contributing to excessive stress or strain on thewindow pane to minimize the risk of breakage (during normal operation,and considering, for example, someone pulling on the device after it isoptically coupled to the window).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows orthogonal views of a toroidal prism, and its location inan end-application that utilizes a side-emitting LED.

FIG. 1A is an enlarged elevation view of the side-emitting LED shown inFIG. 1, which is a Luxeon III side-emitting LED.

FIG. 1B is a graph of a typical spatial radiation pattern of theside-emitting LED shown in FIG. 1A.

FIG. 2 shows a prism symmetrical about an axis central with respect tothe prism specifically designed for use with a LED having a lambertianangular distribution.

FIG. 3 shows the x-y coordinates of the curvature of the optical surfaceof the prism in FIG. 2.

FIG. 3A shows an exemplary slab diverter approach to focus theomnidirectional light from the toroidal prism with a 90 degree arc ashighlighted in the Figure.

FIG. 4 shows an alternate embodiment, whereby a LED is placed on oneside of a window, and a reflective optic is aligned and opticallycoupled to the opposite side.

FIG. 5 shows equations used in analysis of traditional edge-lightingapproach for a light guide, receiving light into its entrance surface S1from a LED having a lambertian angular distribution.

FIG. 6 shows analysis results for light guide of FIG. 5 having arefractive index of 1.51. Note that the light rays for all anglesreflect off the sidewalls S2 and S4 via total internal reflection (TIR).However, all angles also exit surface S3, opposite entrance surface S1.Note also that the incident angles at surface S2, identified as (90−θ2)are restricted to angles between 48.53 and 90 degrees. As discussedpreviously, for the geometry shown in FIG. 5, it is physicallyimpossible for rays to strike surface S2 between the critical angle, asin(n3/n2)=41.47 degrees, and its complement, (90−41.47)=48.53 degrees.This physical limitation does not exist for the inventive approach shownin FIG. 7, discussed directly below.

FIG. 7 shows equations used in analysis of prism-coupled approach for alight guide, receiving light into its entrance surface S1 from aside-emitting LED having, such as those available from Lumileds. Notethat the angular distribution chart from Lumileds shows a smallproportion of the light exiting the LED in the vertical direction(corresponding to 0 degrees on the chart), and the amount getsprogressively higher as the angle gets closer to 90 degrees on eitherside of the vertical axis. Therefore, ψ=0 degrees on the drawingcorresponds to +/−90 degrees on the Lumileds chart, and is so-annotated.

FIG. 7A shows a Luxeon III side emitting LED angular distribution.

FIGS. 8A and 8B show analysis results for approach in FIG. 7 having arefractive index of 1.51, a prism refractive index of 1.49, and a prismangle, α, of 7 degrees. FIG. 8B continues the table shown in FIG. 8Afrom the bottom of the table shown in FIG. 8A. Note that the light notonly TIRs off of side S2 for ψ=0 to +90 degrees (see column for θ3), butmuch of the higher intensity light also TIRs off of side S3, oppositeentrance surface S1, for ψ=0 to +20 degrees. This is because incidentangles at surface S2, identified as (90−θ2) can go as low as 42.09degrees for ψ≧0 in the configuration shown in FIG. 7 (as opposed to48.53 degrees in FIG. 6), and thus there exists a range of incidentangles, (90−θ2), at S2 between the critical angle, 41.47 degrees, andits complement, 48.53 degrees. The table shows that rays can TIR off ofboth surface S2 and S3, allowing light to propagate through arectangular slab light guide (with polished faces for maximumefficiency) until the light has been extracted or dissipated. This isboth significant and unexpected, and is further exemplified in FIGS.9A-11B, wherein TIR is achieved at both S2 and S3 when the incidentangle at S2 is between the critical angle and its complement. Finallynote that in FIGS. 8A and 8B, the last column in the table identifiesthat the extreme angles of ψ (25 to 90 degrees) will leak out of surfaceS3 (and S1), thereby requiring, e.g. a specular reflector on surface S3(and S1) if these rays must be preserved with the light guide.

FIGS. 9A and 9B show analysis results for the approach in FIG. 7 for aprism angle, α, of 14 degrees. FIG. 9B continues the table shown in FIG.9A from the bottom of the table shown in FIG. 9A. Note the differencesin angles of ψ by which TIR can be achieved at surfaces S2 and S3 (andtheir opposing faces due to symmetry) when compared to other angles ofα.

FIGS. 10A and 10B show analysis results for the approach in FIG. 7 for aprism angle, α, of 21 degrees. FIG. 10B continues the table shown inFIG. 10A from the bottom of the table shown in FIG. 10A. Note thedifferences in angles of ψ by which TIR can be achieved at surfaces S2and S3 (and their opposing faces due to symmetry) when compared to otherangles of α.

FIGS. 11A and 11B show analysis results for the approach in FIG. 7 for aprism angle, α, of 28 degrees. FIG. 11B continues the table shown inFIG. 11A from the bottom of the table shown in FIG. 11A. Note thedifferences in angles of ψ by which TIR can be achieved at surfaces S2and S3 (and their opposing faces due to symmetry) when compared to otherangles of α.

FIG. 12A shows an alternate embodiment using a collimated LED with anauxiliary ‘diverter’ used to transform the angles into appropriateangles for use by the prism. The term ‘diverter’ connotes a functionalrepresentation, wherein the actual optical element can be reflective (asshown), refractive, diffractive, etc.

FIG. 12B shows essentially the same arrangements as in FIG. 12A, exceptthat the ray propagation is reversed, with the prism used to collectlight from the light guide and funnel into a photodiode.

FIG. 12C shows the use of a non-imaging optic (shown as a formed sheetmetal reflector, but can also be refractive) to collimate ambient light(provided via an optical fiber) to be used as the source instead of aLED (or laser diode, etc). The Figure also shows the use of laminatedglass window, consisting of two sheets of ¼″ glass (such as low-ironStarphire from PPG) bonded via a layer of poly vinyl butyral (PVB). Therefractive index of PVB must be considered in determining whether lightwill traverse the PVB layer, or reflect via TIR.

FIG. 13 demonstrates various methods by which rays can be extracted fromthe window or light guide. The first extraction feature, EF1, could bethe ink from a fluorescent marker. EF2 is a lens-like diffusing elementattached to window film WF1, coupled to the window via adhesive film,AF1. EF3 is a scattering particle or a void with the bulk of the lightguide. Some scattered rays will exit the window like ray RF, whileothers will TIR, like ray RG. EF4 is a surface divot that could beachieved via etching, sandblasting, or other methods used to removematerial from the surface of the window.

FIGS. 13A-13F show and describe various extraction mechanisms thatprovide indicia illuminated by the window (via an optically coupledinner layer) and optionally indicia on an optically isolated (to apredefined degree, not necessarily 100% isolated) outer layer. Inparticular, FIGS. 13E and 13F show that exemplary mosquito netting canact as an excellent optical isolation layer since the netting has largevoids and since the fibers tend to be rounded, only making point contactwith the inner layer film, thereby also minimizing the potential foroptical contact. The netting is typically polyester. Further, a daytimenon-illuminated image may be imparted to the netting if desired, such asvia dye sublimation printing, known for its compatibility withpolyester. FIG. 13F shows a window cling optically coupled to a window.

In addition to the use of cling vinyl films and electret films, othermethods separately or in combination, are contemplated by which thelight guide and inner/outer layers of an extraction mechanism can beheld in a predetermined spatial relationship (static or relativetranslation/rotation), such as mechanical fastening, chemical bonding,and forces induced by gravity, magnetism, surface tension, suction, etc.Such methods can be distributed across the surfaces of the layers inperiodic/aperiodic fashion. Optical losses may be considered as certainmethods will induce haze, absorption or otherwise seemingly lossyattributes. Note that in some instances, what might seem to be a lossyattribute actually imparts a desired effect, aesthetic or otherwise.

It is also contemplated that when there are inner and outer layers, theycan be optically isolated (at one or more points) such as a dual panethermal window, or by such use of air-spaced (or other low refractiveindex) structures as demonstrated in microstructured adhesives, bubblewrap, corrugated plastic sheets, thermal formed plastic sheets,transparent insulation such as honeycomb structures, placement of anintervening mesh or netting, spacer beads/rods/fibers, printed spacers,foams, adhesive dots, or simply ink dots dispensed using the same inkand inkjet printer as used for the inner/outer layers ensuring a cureddot height sufficient for optical isolation.

The inner layer may be optically coupled to the window (light guide) viaan adhesive (continuous layer or distributed over preselected areas), orsimply as a function of its smooth surface (cf. the '221 referencedabove) and static cling. Similarly, the inner layer can be opticallyisolated from the window (light guide) in selected areas by a low indexmaterial (e.g., TEFLON) and/or by physical separation to avoidevanescent coupling (e.g., via surface roughness, printed dots,mechanical deformation, etc.).

Light redirecting optical films are known (see e.g., U.S. Pat. No.7,090,389). It is contemplated that these structures, or derivativesthereof, can be optically coupled to the surface of a window in order toredirect light within the window to guide it more towards an area ofinterest.

FIG. 14 shows equations used in analysis of prism-coupled approach for alight guide, similar to that shown in FIG. 7, except a couplingmaterial, CM1, of refractive index n6, is included in the analysis.

FIGS. 15A-1 and 15A-2 show the influence on the refractive indices of afirst material (e.g., prism) and a second material (e.g., couplingmaterial) to determine whether light rays of a given incidence angle atthe boundary between the materials will TIR. Steps 1 through 3 aredescribed on the Figures. FIG. 15A-2 continues the table shown in FIG.15A-1 from the bottom of the table shown in FIG. 15A-1.

FIGS. 15B-1 and 15B-2 provide an analysis of the relative angles when avinyl window film is deployed in the stackup arrangement shown in FIG.15B-3. Note that the analysis of water coupling is referenced in FIG.15A-2 (step 4). FIG. 15B-2 continues the table shown in FIG. 15B-1 fromthe bottom of the table shown in FIG. 15B-1.

FIG. 16 shows detailed cross-sectional view of a mall windowapplication, with prisms and LEDs integrated into window clamps.

FIG. 17A shows a front view of a mall window in FIG. 16, also showing aLED driver, with a wireless communications link to a remote PC, whichcan be used to control the intensity vs. time profile of the LEDs. Inone exemplary embodiment, the profile is coordinated between a pluralityof windows (and other sources of light and sound).

FIGS. 17B-17E show front views of four adjacent mall windows, each witha unique number of LEDs illuminated using prism coupling.

FIGS. 17F-17I show front views of four adjacent mall windows, each witha unique number of LEDs illuminated using traditional edge coupling.

FIGS. 18A-1, 18A-2, 18A-3, 18A-4, 18B-1, 18B-2, 18B-3, 18B-4, 18C-1,18C-2, 18C-3, 18C-4, 18D-1, 18D-2, 18D-3, 18D-4, 18E-1, 18E-2, 18E-3,18E-4, 18F-1, and 18F-2 show x/y coordinates (and intermediatecalculations) of the surface profile shown in FIG. 3. Each of FIGS.18A-2, 18B-2, 18C-2, 18D-2, 18E-2, and 18F-2 continues the table shownin FIGS. 18A-1, 18B-1, 18C-1, 18D-1, 18E-1, and 18F-1, respectively,from the right side of the table shown in FIGS. 18A-1, 18B-1, 18C-1,18D-1, 18E-1, and 18F-1, respectively. Each of FIGS. 18A-3, 18B-3,18C-3, 18D-3, and 18E-3 continues the table shown in FIGS. 18A-1, 18B-1,18C-1, 18D-1, and 18E-1, respectively, from the bottom of the tableshown in FIGS. 18A-1, 18B-1, 18C-1, 18D-1, and 18E-1, respectively. Eachof FIGS. 18A-4, 18B-4, 18C-4, 18D-4, and 18E-4 continues the table shownin FIGS. 18A-2, 18B-2, 18C-2, 18D-2, and 18E-2, respectively, from thebottom of the table shown in FIGS. 18A-2, 18B-2, 18C-2, 18D-2, and18E-2, respectively, and each of FIGS. 18A-4, 18B-4, 18C-4, 18D-4, and18E-4 continues the table shown in FIGS. 18A-3, 18B-3, 18C-3, 18D-3, and18E-3, respectively, from the right side of the table shown in FIGS.18A-3, 18B-3, 18C-3, 18D-3, and 18E-3, respectively. Note that otherprofiles than that shown in FIG. 3 are contemplated, and are influencedby the material properties discussed herein, and tradeoffs imposed bydesign constraints (e.g., size vs. coupling efficiency, etc).

FIGS. 19A and 19B show objects illuminated with the instant invention,detailing a variety of indoor and outdoor applications. Note that thetic-tac-toe annotations on each object indicate where the light isextracted. Note that the mailbox is a formed sheet of a transparentpolymer.

FIGS. 20A-1 and 20A-2 show an exemplary flexible solar-cell and anexemplary solar-cell based light controller, respectively, for use in aremote mailbox application further detailed in FIGS. 20B-1 and 20B-2.

FIG. 20B-1 shows a rural mailbox with representative dimensions shownthereon. FIG. 20B-2 is a large size mailbox shell in a flattenedcondition in order to detail the position of various elements asdetailed in the drawing.

FIG. 21A shows the use of a commercially available secondary lens forLEDs that converts a lambertian distribution into a side-emittingdistribution. FIG. 21B shows enlarged perspective views from the bottomand the top of the commercially available secondary lens for LEDs. FIG.21C shows a plot of the full width at half maximum (FWHM) divergenceversus side emitter rotation angle (azimuthal) for the commerciallyavailable secondary lens for LEDs shown in FIGS. 21A and 21B. FIG. 21Dshows the luminous intensity in Candela (Cd) at a side emitter rotationangle of zero degrees azimuth for the commercially available secondarylens for LEDs shown in FIGS. 21A and 21B. The minimum luminous intensityshown in FIG. 21D is 1.592 Cd, the maximum luminous intensity shown inFIG. 21D is 33.4 Cd, the average luminous intensity is 6.55 Cd, and theFWHM in FIG. 21D is 8.95 degrees. FIG. 22A shows the use of thecommercially available secondary lens for LEDs that converts alambertian distribution into a side-emitting distribution for use by atoroidal prism. FIG. 22B is an enlarged view of the LED and its mountingshown in FIG. 22A.

FIG. 23A shows a prior art diffusing film comprising resin particles ina binder. As the resin dries, it forms an undulating surface, followingthe contours of the bead-like particles.

FIG. 23B provides a first order optical analysis of the effects of thediffusing film in FIG. 23A when receiving light at an angle of δ(relative to the horizontal axis shown) via a window (not shown).

FIGS. 24A and 24B show the relative intensity out of a Lumiledslambertian and side emitting LED, respectively. Portions of theseintensity curves were modeled in Excel as shown in FIG. 24C.

FIGS. 25A-1 and 25A-2 detail the angle, φ, that light leaves thediffusing screen in FIG. 24B as a function of the incident angle, δ, andthe slope of the diffusing surface, γ, as detailed in FIG. 23B. Notethat the incident angle, δ (third column of FIGS. 25A-1 and 25A-2) mapsto (90−θ2) in FIGS. 5 and 7, respectively, which maps to θ1 and ψ(second column of FIGS. 25B-1 and 25B-2, respectively) coming from theLEDs in those figures, respectively. Also shown in the first column ofFIGS. 25A-1 and 25A-2 is the relative intensity of the LEDs in FIGS. 5and 7, respectively, as a function of angles θ1 and ψ, respectively.Note that for certain combinations in the table (denoted by ##TIR##),the light striking the undulating surface of the diffuser cannot exit,and is reflected back into the diffuser via TIR. The ultimate fate ofthese rays can be determined by any suitable ray trace program as isknown in the art.

FIGS. 25B-1 and 25B-2 are similar to FIGS. 25A-1 and 25A-2,respectively, except that they provide additional granularity aroundthose conditions causing TIR at the undulating surface of the diffusingfilm.

FIG. 26A demonstrates the intensity of those rays exiting the diffuserfilm for a traditional edge light approach, with each successive curveindicating a different slope, γ, at the exit surface of the diffuser.Slope values are annotated for γ values of 7.1 degrees, 7.9 degrees,etc.

FIG. 26B demonstrates the intensity of those rays exiting the diffuserfilm for the prism coupling approach, with each successive curveindicating a different slope, γ, at the exit surface of the diffuser.Slope values are annotated for γ values of −39.1 degrees, −32.5 degrees,etc.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring to FIG. 1, a window or other transparent substrate 10 is tohave light from an LED 20, which is a semiconductor that emits light inresponse to electrical stimulation transmitted into the transparentsubstrate at angles related to the material of the substrate so that thelight is “trapped” within the substrate as a result of total internalreflection (i.e., TIR) off the inside of the exterior surfaces of thesubstrate. Propagation of the light continues within the transparentsubstrate until it has been fully absorbed/extracted.

In a preferred form, an LED 20 preferably of the side-emitting type ispositioned on a support and heat sink 22 near to a side surface of thesubstrate 10 to deliver the light that is to enter the substrate.Additional sources of light might include a fluorescent material or aphotoluminescent material, which are conventionally stimulated to emitlight.

In order to cause the light from the LED to enter the substrate (i.e.,window pane), an optical coupling arrangement 30 is provided. As shown,it comprises what has been termed a toroidal prism due to its centralthrough-hole and circular shape.

FIG. 2 shows a prism 30′ symmetrical about an axis central with respectto the prism specifically designed for use with a LED having alambertian angular distribution. The rotationally symmetrical prism 30′has two portions 33, 34 arranged symmetrically with respect to an axis Yabout which symmetrical prism 30′ is symmetric. Portions 33, 34 have agap 38 between them.

FIG. 3 shows the x-y coordinates of the curvature of the optical surfaceof the prism in FIG. 2

FIGS. 18A-1, 18A-2, 18A-3, 18A-4, 18B-1, 18B-2, 18B-3, 18B-4, 18C-1,18C-2, 18C-3, 18C-4, 18D-1, 18D-2, 18D-3, 18D-4, 18E-1, 18E-2, 18E-3,18E-4, 18F-1, and 18F-2 show x/y coordinates (and intermediatecalculations) of the surface profile shown in FIG. 3.

As not all LED manufacturers offer side emitting LEDs, and secondaryside emitting lenses may not be acceptable for a variety of reasons, acustom optic like the cross-section shown in FIG. 2 can be constructedfor use with any LED, obviating the need for a side emitting LED andseparate toroidal prism. In FIG. 2, the optic has been designed toaccept any LED and bend the rays at the required angles into the window.In this particular embodiment, rays from the LED were analyzed tominimize Fresnel reflections, account for draft angles to allow formolding, maintain a compact size, etc.

FIG. 1 demonstrates a one-zone planar input surface; i.e., a constantsurface tangent bounded by the top and bottom surfaces that formdiscontinuous surface tangents.

FIG. 2 demonstrates three zones, each having a smoothly changing surfacetangent and each bounded by at least one discontinuity in the surfacetangent.

The particular design embodiment in FIG. 2 has been subdivided in threeregions or zones −0°˜20°, 20°˜60°, and 60°-90°, with representative raysshown as A, B, and C, respectively. Note that the reflections withinthis circular prism for rays A and C have been accommodated via TIR,although reflective coatings can be employed as desired. Note that thecircular prism needs to be coupled to the window with coupling media.

FIG. 3 shows the profile as calculated in Excel, with the detailedcoordinates and interim calculations shown in FIGS. 18A-1, 18A-2, 18A-3,18A-4, 18B-1, 18B-2, 18B-3, 18B-4, 18C-1, 18C-2, 18C-3, 18C-4, 18D-1,18D-2, 18D-3, 18D-4, 18E-1, 18E-2, 18E-3, 18E-4, 18F-1, and 18F-2.

The prism arrangement has, as its entire surface at 36 facing the LED, aseries of radius curves of the prism, and the radius curves are selectedby one of skill in the art to bend the light emitted by the LED andentering the transparent substrate 10 at angles, for example as in FIG.3, for the light to remain trapped within the substrate between theinternal surfaces. This is shown schematically in FIG. 2. Light from theLED entering the substrate at too large an angle with respect to thesurface of the transparent substrate would pass through the substraterather than being trapped within. It may be blocked by an opaque maskover that part of the substrate.

FIG. 3A shows an exemplary slab diverter approach to focus theomnidirectional light from the toroidal prism with a 90 degree arc ashighlighted in the Figure. When placed on a surface of a window at eachcorner of the window or each corner of rectangular indicia within thewindow, this type of diverter optic concentrates the light to the areaswhere it is needed. Other arc angles can be selected to obtain a desiredeffect. While FIG. 3A shows a parabolic diverter for use with certainrays, other forms are contemplated, such as linear, multifaceted,elliptical, circular, CPC (compound parabolic concentrator, a genericreference herein to non-imaging optics), or some combination thereof.

The diverter can be constructed so that it can be rotated when opticallycoupled through the window (e.g., via optical grease or oil, similar toan optical slipring) or alternatively, coupled via an air gap or lens(array) from a rotating diverter through a secondary optic (e.g.,circular prism) that is affixed and optically coupled to the window.This allows the light distribution within the glass to be optimized forthe desired aesthetic effects; e.g., uniform illumination of new indiciathat are optically coupled to a window, where the extraction of lightthrough prior indicia is markedly different than the new indicia. Notethat instead of a single side-emitting LED with a mechanically rotatingoptic, an array of (semi)collimated LEDs can be substituted herein fortemporally directing the beam through a surface coupled optic.

The attachment to the window can be engineered to allow the diverter torotate in order to adjust the direction of light within the window tobest suit an application. For example, a clear vinyl can be coupledfirst to the window, and then coupled to the diverter via optical greaseto allow movement without losing the optical coupling. Further, facetedstructures can be added to the toroidal prism (the one shaped like athick, countersunk flat washer). For example, the outer circumferencecan comprise facets over certain portions, redirecting light asappropriate. The outer circumference can also be coated or surrounded bya specular reflector. Certain portions of the top surface can compriseprismatic-like features to redirect light as needed. These features canbe subtractive-from and/or additive-to to the top surface of thetoroidal prism. The top can also be de-coupled (optically) in selectlocations to allow reflections from the opposing side to propagate intothe window without bouncing back into the diverter.

The side-emitting optic itself can be partially surrounded by a specularreflector, intercepting certain rays and redirecting them to anothercanted prism input face. This could be of use if an application uses athin window, and the light is to be concentrated within a certainangular zone.

The light that passes straight up from the LED 20 through the substrate10 at a too large angle to be trapped inside the substrate may be usedin the substrate by positioning a coupling arrangement in the form of areflective optic, of the type shown in FIG. 4, for example filled with acoupling medium, at the other surface of the substrate from the LED. Theoptic 50 is shaped so that the optic will reflect impinging light backinto the substrate and at an angle where that light would then betrapped within the substrate as well.

FIG. 4 shows an alternate embodiment, whereby a LED is placed on oneside of a window, and a reflective optic is aligned to the oppositeside.

In order to show breadth of the invention, the approach in FIG. 4optically couples an LED chip on one face of a window, and opticallycouples a reflective optic on the opposing face. The coupled LED, aspreviously discussed, allows all angles to exist within the window.Those angles that would naturally TIR from the opposing face of thewindow are not intercepted by the reflective optic. Those angles thatwould pass through the window naturally are redirected by the opticallycoupled reflective optic into angles that TIR between the opposingfaces. No effort has been made to optimize the angles to maximize theopportunity for TIR at the end faces of the window (not shown). Such adesign is contemplated and can be fashioned by one of skill in the art.

An advantage to this approach is that the reflective optic naturallyblocks all light that would leak through the opposing face (note theadditional light blocking layer above the LED in FIG. 7).

FIG. 12A shows an alternate embodiment using a collimated LED with anauxiliary ‘diverter’ used to transform the angles into appropriateangles for use by the prism. The term ‘diverter’ connotes a functionalrepresentation, wherein the actual optical element can be reflective (asshown), refractive, diffractive, etc.

An advantage of this approach is that widely available collimated LEDs(and laser diodes) can be used, and a reflective diverter can beemployed to change the beam's direction to that of a side-emitting LED.A reflective diverter also acts to block any light from leaking throughopposing face, S3.

FIG. 12B shows essentially the same arrangements as in FIG. 12A, exceptthat the ray propagation is reversed, with the prism used to collectlight from the light guide and funnel into a photodiode.

As previously mentioned, non-imaging concentrators can be used inreverse as collimators. The same is true here, where the circular prismis used in the reverse sense to collect light trapped within the window.Note that the other toroidal and circular prism couplers can be used inthe sensor mode as well. It is also contemplated that combinationsource/sensors can be deployed (e.g., via beamsplitters). For example,light from an external communications source can be coupled into thewindow via a holographic optical element (HOE) as taught in U.S. Pat.No. 6,724,508, and sensed by the instant invention via toroidal/circularprism couplers.

FIG. 12C shows the use of a non-imaging optic (shown as formed sheetmetal reflector, but can also be refractive) to collimate ambient lightto be used as the source instead of a LED (or laser diode, etc). Thefigure also shows the use of laminated glass window, consisting of twosheets of ¼″ glass (such as low-iron Starphire from PPG) bonded via alayer of poly vinyl butyral (PVB). The refractive index of PVB must beconsidered in determining whether light will traverse the PVB layer, orreflect via TIR.

As shown in FIG. 12C, remote sources of light such as sunlight, roomlight, an optical communications signal, light from an optical fiber,etc. can be coupled into the window. Other optical approaches arecontemplated, either as a substitute or complement to the collimatingnon-imaging optic shown in FIG. 12C.

FIG. 4 illustrates the optic 50 at the substrate without the arrangement30. They may be used as separate alternatives or may be used incombination at a particular installation. In the latter situation, thelight passing across the substrate is not masked, but is permitted toimpinge on the optic 50.

FIG. 7 shows equations used in analysis of prism-coupled approach for alight guide, receiving light into its entrance surface S1 from aside-emitting LED having, such as those available from Lumileds. Notethat the angular distribution chart from Lumileds shows a smallproportion of the light exiting the LED in the vertical direction(corresponding to 0 degrees on the chart), and the amount getsprogressively higher as the angle gets closer to 90 degrees on eitherside of the vertical axis. Therefore, ψ=0 degrees on the drawingcorresponds to +/−90 degrees on the Lumileds chart, and is so-annotated.

FIG. 14 shows equations used in analysis of a prism-coupled approach fora light guide, similar to that shown in FIG. 7, except that a couplingmaterial, CM1, of refractive index n6, is included in the analysis.

FIGS. 15A-1 and 15A-2 show an analysis of the influence on therefractive indices of a first material (e.g., prism) and a secondmaterial (e.g., coupling material) to determine whether light rays of agiven incidence angle at the boundary between the materials will TIR.Steps 1 through 3 are described on the Figures.

FIGS. 15A-1 and 15A-2 detail an exemplary approach in the choice ofappropriate coupling media for an acrylic prism (n=1.49) trying to passangles up to 75 degrees off-normal through the coupling media, and thusrequiring a minimum refractive index of 1.44 for the coupling media(e.g., acrylic PSA, n=1.47, P/N ARClear 8154 from Adhesives Research).

An interesting application is the case of a vinyl window decal that iswater-coupled to a window. Water has a refractive index of about 1.37 at300 nm, down to 1.33 at 670 nm. Clear vinyl window cling is a PVCmaterial, and PVC has a refractive index of 1.54. As shown in FIGS.15B-1 and 15B-2, the angle within the clear vinyl, θ2, from an acrylicprism (α=7°), and coupling media of the same index, is <50° (to ensureTIR at both S2 and S3). As shown in callout box #4 in FIG. 15A-2, theminimum index for the coupling media between the vinyl and the windowglass must be about 1.18, and therefore water satisfies the constraint(for the wavelengths for which 1.54 is the index of vinyl). Thisnon-limiting example demonstrates that water can couple light from aclear vinyl window cling into window glass when a prism is coupled intothe vinyl as shown in the stackup in FIG. 15B-3. A significant advantageof the window cling approach is the simplicity of installation (andremoval), allowing use of the invention by both novice and professionalinstallers.

The toroidal prism, TP1, shown in FIG. 7 has smooth surfaces, and is inthe general shape of a thick flat washer with a countersunk centralthrough-hole. The side emitting LED provides a semi-collimated beamabout a plane orthogonal to the vertical axis through the center of theLED as shown in the graph of FIG. 7A (based on a Luxeon LED). Note fromthe graph that there is some residual light at all other angles, some ofwhich will not TIR and thus leak through the window. Note in FIG. 7 thatdirectly above the top side of the LED there is a reference to ablocking film.

As stated previously, for a window with n=1.51, light will TIR from bothfaces S2 and S3 if −48.53°<θ2<−41.47° and 41.47°<θ2<48.53° (where thenegative angles indicate those angles reflected about the axis normal toS2 or S3). This is detailed in FIGS. 8A and 8B, which are based on aconfiguration of a toroidal prism like that in FIG. 7 with α=7° and0°≦ψ≦20°. Note that the designer must be mindful of Fresnel reflectionsof ray R1A relative to prism face S6 as the incident angles can be closeto grazing where the Fresnel reflections become substantial.

Note also that this type of side emitting LED is not offered by everyLED manufacturer. There are secondary lenses, e.g., P/N 10267 availablefrom Carclo Technical Plastics, 111 Buckingham Avenue, Slough, BerkshireSL1 4PF England/600 Depot Street, Latrobe, Pa. 15650 USA, telephone UK:0044 (0) 1753 575011, Telephone USA: 00 (1) 724 539 6982, 84 shown inFIGS. 21A and 21B. Note, however, the size is much larger than that ofthe integrated lens in the Lumileds part, and so it may be moredifficult to deploy, either from a mechanical packaging perspective orfrom the optical principle of etendue (describes the fundamental limitgoverning the amount of light that can be coupled from a given sourceinto a system; see for example, US 2008/0212328). So, a window of agiven thickness and refractive index can only accept a certain amount oflight via prism coupling based upon the etendue of the optical system(LED+optics). FIG. 21A shows side-emitting optic 84 assembled on luxeonLED 86, a clear acrylic or polycarbonate sheet 90 being positioned onboth sides of the assembly of the side-emitting optic 84 and the luxeonLED 86. The average FWHM of the side-emitting secondary optic 84 is 8.4degrees, the minimum FWHM is 7.45 degrees, and the maximum FWHM is 9.3degrees. The efficiency of the side-emitting secondary optic 84 is 87%and Cd/lm is 38/46=0.8 @ 350 mA (based on an average of eight readings).FIG. 22A shows the commercially available secondary lens 84 for LEDsthat converts a lambertian distribution from LED 98 into a side-emittingdistribution for use by a toroidal prism 92. The commercially availablesecondary lens 84 is bounded by a specular reflector 94, the toroidalprism 92, and air 88 between the specular reflector 94 and the toroidalprism 92, the toroidal prism 92 having an underside angle 96 with thehorizontal of 7 degrees. Air 88 is also present below the specularreflector 94. As shown in FIG. 22B, LED 98 is mounted on a FR4 board 100and aluminum board 102.

FIGS. 7 though 11B demonstrate the effects of the prism angle, α, on theangles of ψ for which TIR can be achieved at both S2 and S3.

In FIGS. 8A and 8B, α=7°, and assuming the LED emission is containedwithin 0°≦ψ≦20°, TIR is achieved, quite unexpectedly, at both surfacesS2 and S3. This provides a significant boost in efficiency, as TIR iseffectively lossless. It thus precludes light leakage at the edges ofthe window (if that is a requirement as opposed to an effect that isdesirable for a given application).

In FIGS. 9A and 9B, 10A and 10B, and 11A and 11B, α is set to 14°, 21°,and 28°, respectively. The tables show, amongst other things, thetradeoffs between leakage and reflection at S2 and S3 depending upon therange of angles from the LED, ψ.

Finally, other factors can be optimized via ray trace programs, such asFresnel reflections, skew rays, etc. Further, it is contemplated thatthe prism surfaces can deploy faceted geometric features, diffractivefeatures, etc, in order to direct the beams into the window in one ormore preferred directions, increase coupling efficiency into the window,or optimize any other price/performance target. It is also contemplatedthat an element can be placed on the opposite side of the window fromthe prism in order to block light (can be air gapped), redirect the beam(optically coupled), or become illuminated by any light leakage foreffect or other predetermined purpose. Examples appear in FIG. 4. Notealso that the prism angle, α, can be varied within the same part inorder to optimize performance for a given application. Also, a portionof the prism can be replaced with a reflective optical feature toredirect light in one or more preferred directions. An example of suchas system is taught in U.S. Pat. No. 6,565,235. For example, a reflectorcan surround 270° of a side-emitting LED, redirecting incident lighttowards the opposing side so that light side-emits around only a 90°swath. This would be useful in an application where the prism is couplednear the corner of a window, directing the light within the windowthrough a 90° sweep, from rays parallel to one edge of the window tothose parallel to the adjacent (orthogonal) edge (in the case of arectangular window). In other applications, a collimated LED can beprism-coupled to direct light along a preferred narrow path within thewindow. In fact, an array of LEDs can be so-coupled and arranged along aline, in a radial pattern, or any other configuration to achieve theprice/performance so desired. Such an array (UV LEDs for fluorescentfilms, visible LEDs for diffusing films, and combinations thereof) canbe time-sequenced (intensity and/or color) to achieve interesting visualeffects.

FIGS. 8A and 8B show analysis results for the approach in FIG. 7 havinga refractive index of 1.51, a prism refractive index of 1.49, and aprism angle, α, of 7 degrees. Note that the light not only TIRs off ofside S2 for all values of ψ, (see column for θ3), but significantly, andquite unexpectedly, light also TIRs off of side S3, opposite entrancesurface S1, for ψ=0 to +20 degrees. This is because incident angles atsurface S2, identified as (90−θ2) can go as low as 42.09 degrees (asopposed to 48.53 degrees in FIG. 6). For those rays that can TIR off ofboth surface S2 and S3, light will propagate through a rectangular slablight guide (with polished faces to avoid TIR-defeating scatteringsites) until the light has been extracted or dissipated.

FIGS. 9A and 9B show analysis results for the approach in FIG. 7 forprism angle, α, of 14 degrees. Note the differences in angles of ψ bywhich TIR can be achieved at surfaces S2 and S3 (and their opposingfaces due to symmetry) when compared to other angles of α.

FIGS. 10A and 10B show analysis results for the approach in FIG. 7 forprism angle, α, of 21 degrees. Note the differences in angles of ψ bywhich TIR can be achieved at surfaces S2 and S3 (and their opposingfaces due to symmetry) when compared to other angles of α.

FIGS. 11A and 11B show analysis results for the approach in FIG. 7 forprism angle, α, of 28 degrees. Note the differences in angles of ψ bywhich TIR can be achieved at surfaces S2 and S3 (and their opposingfaces due to symmetry) when compared to other angles of α.

In order for light to pass through the prism and into the window, theprism must be optically coupled to the window surface via a couplingmedium 54 therebetween. Examples of optical coupling media are providedabove. The coupling medium fills any minimal gap between the opposingsurfaces of the prism or other optic and the substrate so that all lightemerging from the prism or other optic will pass through that medium tothe substrate.

The light is transmitted along the transparent substrate and does notemerge and is not visible outside the substrate. The purpose of thisinvention is to enable illumination of locations 60 on the substrate, tocreate letters or images or the like (i.e. indicia). At locations wherethe transparent substrate should have a visible illuminated area,something is placed on or performed on the substrate as at 60 to scatterlight that impinges upon it from inside the substrate. As noted above,this may comprise dots printed on the substrate at locations to createan image, glass beads, fluorescent inks, roughened area of the surface,etc., whatever would cause light to scatter and exit the substrate bydefeating TIR. This enables the substrate or window to be used forproviding information, decoration, etc. by characters, figures, etc.that appear to be illuminated at the transparent substrate. This is anesthetically interesting and pleasing way of providing information ordecoration.

FIG. 13 demonstrates various methods by which rays can be extracted fromthe window or light guide. The first extraction feature, EF1, could bethe ink from a fluorescent marker. EF2 is a lens-like element attachedto window film WF1, coupled to the window via adhesive film, AF1. WF1can also be a grazing incidence hologram as taught in U.S. Pat. No.5,710,645. EF3 is a scattering particle or a void with the bulk of thelight guide. Some scattered rays will exit the window like ray RF, whileothers will TIR, like ray RG. EF4 is a surface divot that could beachieved via etching, sandblasting, or other methods used to removematerial from the surface of the window.

FIG. 16 is a detailed cross-sectional view of a mall window with prismsand LEDs integrated into window clamps.

Note from this figure that optical coupling into the compliant foamwithin the window clamps should be minimized to avoid defeating TIR andcausing absorption into the foam. This foam is used to better distributethe clamping pressure to the glass, avoiding any excess pressure on theglass that might lead to fracture. Also note that heat from the LEDsneed to be considered, and can be conducted away through the windowclamp and into the support tube. The transient and steady statetemperatures can be predicted by suitable thermal analysis programs suchas ANSYS Thermal Analysis System, and the general analytic approachesare taught in “Cooling Techniques for Electronic Equipment, 2ndEdition”, D. Steinberg, ISBN 0471524514.

An optically coupled window film shown in FIG. 16 is subdivided inpieces. This represents, as a non-limiting example, computer cut windowdecals that are optically coupled to the window. These decals preferablycomprise a scattering property such that light can be extracted from thewindow at selected points/areas, such as the lines of text, or a graphicimage. The gaps between the film pieces assist in ensuring uniformity ofthe illuminated image as the light is not quickly extracted from one endof the decal without enough left to reach the center.

FIG. 17A is a front view of a mall window as in FIG. 16, also showing aLED driver, with a wireless communications link to a remote PC, whichcan be used to control the intensity vs. time profile of the LEDs. Inone exemplary embodiment, the profile is coordinated between a pluralityof windows (and other sources of light and sound).

FIGS. 17B-17E are front views of four adjacent mall windows usingcircular/toroidal prism coupling, each window with a unique number ofLEDs illuminated.

FIGS. 17F-17I are front views of four adjacent mall windows usingtraditional edge lighting, each window with a unique number of LEDsilluminated. Note that the angles shown within the windows are limitedto −41.47°<θ2<41.47° in accordance with what's shown in FIG. 6 anddiscussed previously relative to FIGS. 5 and 6. The effects of thislimited angular extent within the window is clearly seen when comparingthe distribution of rays between FIG. 17E and FIG. 17I. The lack ofuniformity in FIG. 17I suggests that additional LEDs are required todistribute the LED flux more evenly across the span of the glass.Further, since edge lighting by definition is confined to sources aroundthe edge, as the window span gets wider, losses within the window(absorption, scatter, etc) makes it more difficult to get enough lightto reach the opposing edge in order that beams from opposing LEDs tooverlap to ensure uniform flux within the window across the span.

In contrast, compare the overlap in beams between FIG. 17C and FIG. 17G,and the void in FIG. 17G between the illuminated LEDs. The edgelitapproach is thus very sensitive to both the height and width of thewindow span. To compensate, additional LEDs can be placed along theedge, assuming that the light can travel across the span with sufficientintensity. The prism approach, conversely, can be placed anywhere on thewindow span—near the edge, in the middle, etc., minimizing the number ofLEDs needed, and therefore minimizing both the installation cost, andthe cost of energy supplied to the LEDs.

The general direction of the rays in FIGS. 17F-17I go from left-to-rightand right-to-left, with no rays within the window above or below 45°from the horizontal (prior to extraction). This limited angulardiversity ultimately translates into a limited diversity of rays uponextraction using commonly available (and low cost) diffusing type films.Conversely, the angular diversity of rays within the approach shown inFIGS. 17B-17E provide a more widely viewable indicia when extracted viathe same diffusing film.

As an example, consider a diffusing film of the prior art as shown inFIG. 23A, based on FIG. 1 of Kimura et al., U.S. Pat. No. 6,771,335.This film comprises resin particles 104 dispersed in a resin binder 106with a top surface 108, both having similar refractive indices. Thediffusing properties mainly result from the undulated surface profilesince it is assumed, based on Kimura et al., that an incident ray oflight is not deflected by the resin particles 104, (Kimura et al.provides in column 2, lines 11-13, that, “[f]urther, in the lightdiffusion sheet of the present invention, the difference betweenrefractive indices of the binder resin and the resin particles ispreferably 0.05 or less.”). In FIG. 23B, there is a magnified section ofFIG. 23A along with the geometric implications following Snell's Law. Itshows that for a ray traveling within the plane of the window, strikingthe diffusing surface (e.g., n1 110 being equal to 1.51, the same as thewindow, for simplicity) at an angle, δ 112, it will be redirected intothe air (n2 114 being equal to 1.0) at an angle, relative to the surfacenormal of the window, of φ 116 being equal to γ 118 plus β 120 which isequal to {γ+a sin [(n1/n2)sin(90−δ−γ)]}, where γ 118 is the slope of thediffusing surface relative to the plane of the window.

The light coupled into the window can also be made to vary in time usinga timing device connected to the LED, for example, by an adjustableshade on the optic or rotating the optic for example and over differentareas of a window.

Another variable to consider is the intensity of the rays. FIG. 24Ashows the intensity distribution of light rays exiting a lambertian LED(Lumileds Luxeon III). The highest intensity is at 0° (perpendicular tothe LED die), and it then falls off in a˜cosine distribution. For thisexample, the distribution from 0° through 90° has been approximated bythat indicated in FIG. 24C, which is identified as θ1 in FIG. 5.Similarly, the intensity distribution of light rays exiting from a sideemitting LED (also Lumileds Luxeon III), is shown in FIG. 24B. As withthe lambertian LED, 0° represents the angle perpendicular to the LEDdie. In this case, the peaks are near ±80° (hence the termside-emitter), and the distribution from −90° to 0° has beenapproximated by that indicated in FIG. 24C, except the angulardisplacement has been shifted to start at 0° to be consistent with ψ inFIG. 7A.

Looking back to FIG. 23B, δ represents (90−θ2) in both FIG. 5 and FIG. 7(angle within the window, relative to axis AX2, at which the light rayis incident on surface S3, upon which the diffuser is affixed).

FIGS. 25A-1 and 25A-2 detail both the angle, φ (columns 5, 7, 9, . . .21, 23), and intensity of the rays exiting into air (n1=1.0) from thediffuser (n=1.51) as a function of the incident angle, δ (column 3), andthe slope, γ (columns 4, 6, 8, . . . 20, 22), of the diffuser exitsurface.

FIG. 25A-1 is the solution for the lambertian LED with an air gap to anedgelit window (i.e., FIG. 5), and FIG. 25A-2 is the prism solutionutilizing a side-emitting LED (i.e., FIG. 7).

Column 1 of FIGS. 25A-1 and 25A-2 indicates the normalized intensityprofiles, shown in FIG. 24C, for both the lambertian and side-emittingLEDs, respectively. Recall that the angle δ in column 3 of FIGS. 25A-1and 25A-2 represents the angle of the LED shown in FIG. 24C afterpropagating into the refractive media of the window; i.e., (90−θ2) inboth FIGS. 5 and 7. Particularly noteworthy is the larger anglesavailable with the prism approach as evidenced by Column 3.

FIG. 25B-1 shows that rays from the edgelit approach require a minimum7.9° surface slope, γ, of the diffuser before light begins to emergewithin 90° of normal. FIG. 25B-2 shows that rays from the prism approachrequire a minimum −39.1° surface slope, γ, of the diffuser before lightbegins to emerge.

Note that the ##TIR## entries indicate that for the specified incidentray angle, δ, in column 3, the ray cannot exit the diffuser film at thespecified slope, γ, of the diffuser (it will reflect via total internalreflection).

The data in FIGS. 25A-1, 25A-2, 25B-1, and 25B-2 has been plotted inFIG. 26A for the edgelit approach and FIG. 26B for the prism approach.It is especially noteworthy, and quite unexpected, that the exit anglesout of the diffuser for the prism approach are closer to the surfacenormal than that of traditional edge lighting approach. In fact, thisoff-normal direction has required the use of an additional prismaticfilm in order to straighten-out the exiting rays (Cf. U.S. Pat. No.5,126,882).

Note that in FIG. 26A there is substantial energy outside of φ=90°.Angles beyond 90° will be redirected back towards the plane of windowsurface. Depending upon the system, the rays may travel through the filmand re-emerge either out of the film again, out the opposing side of thewindow, or back into the collection of rays that TIR through the window.Conversely, in FIG. 26B, no energy is outside of φ=90°, which was quiteunexpected.

Therefore, with the prism coupling approach, whether circular, toroidal,or other geometric form, the light introduced into the window will betilted closer to the normal of the window than is possible with edgelighting, thus able to exit via a simple diffusing element (e.g., atranslucent window graphic film) closer to normal.

As a practical example, consider an illuminated graphic on a mallstorefront window located on the second floor of a three floor mallhaving a center atrium. It is desirable to have the graphic viewablefrom shops on all three floors. However, FIGS. 17I and 26A demonstratethat the edgelit approach has less angular diversity within the windowthan the prism approach shown in FIGS. 17E and 26B.

Other uses for the invention besides in a window display might be in aneasel, a posted restaurant menu board, a table top, architecturalwindows, mailboxes, etc., wherever there may be a transparent substrate,an LED and the appropriate coupling arrangement to bring the light fromthe LED through the prism into the window or substrate.

Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art. It ispreferred, therefore, that the present invention be limited not by thespecific disclosure herein, but only by the appended claims.

The invention claimed is:
 1. An apparatus configured to non-invasivelyinject light from a light source into a light transmitting medium havinga first surface portion and a second surface portion directly oppositethe first surface portion, the apparatus comprising: an optic having aplanar exit surface and an input surface, the optic being symmetricalabout a central axis of the optic; and at least one coupling materialadjacent to the planar exit surface and having a refractive indexgreater than air, and configured for optically coupling and physicallyconnecting the planar exit surface to the light transmitting medium; theinput surface being subdivided into one or more regions or zones, eachregion or zone having a constant or smoothly changing surface tangent,and each region or zone being bounded by at least one discontinuity inthe surface tangent so that, when the optic surrounds the light sourceand is optically coupled to the light transmitting medium by the planarexit surface and the at least one coupling material, the optic redirectsa first amount of the light from the light source, that passes throughthe input surface, through the first surface portion, and into the lighttransmitting medium, within a range of angles between a critical angleof the second surface portion and a complementary angle to the criticalangle, and redirects most or all of a remaining amount of the light fromthe light source, that passes through the input surface, through thefirst surface portion, and into the light transmitting medium, at anglesgreater than the complementary angle.
 2. The apparatus of claim 1,wherein the optic is circular.
 3. The apparatus of claim 1, wherein theoptic is toroidal.
 4. The apparatus of claim 1, wherein a cross-sectionof the optic, taken in a plane containing the axis about which the opticis symmetrical, has a gap, a top of the gap being in a plane of theplanar exit face.
 5. The apparatus of claim 4, wherein the gap isbounded by reflective walls in the optic to aid in redirection of aportion of the light from the input surface to the planar exit surface.6. An illumination apparatus configured to non-invasively inject lightinto a light transmitting medium having a first surface portion and asecond surface portion directly opposite the first surface portion, theillumination apparatus comprising: an optic having a planar exit surfaceand an input surface, the optic being symmetrical about a central axisof the optic; a light source, the optic being positioned to surround thelight source; and at least one coupling material adjacent to the planarexit surface and having a refractive index greater than air, andconfigured for optically coupling and physically connecting the planarexit surface to the light transmitting medium; the input surface beingsubdivided into one or more regions or zones, each region or zone havinga constant or smoothly changing surface tangent, and each region or zonebeing bounded by at least one discontinuity in the surface tangent sothat, when the optic is optically coupled to the light transmittingmedium by the planar exit surface and the at least one couplingmaterial, the optic redirects a first amount of the light from the lightsource, that passes through the input surface, through the first surfaceportion, and into the light transmitting medium, within a range ofangles between a critical angle of the second surface portion and acomplementary angle to the critical angle, and redirects most or all ofa remaining amount of the light from the light source, that passesthrough the input surface, through the first surface portion, and intothe light transmitting medium, at angles greater than the complementaryangle.
 7. The illumination apparatus of claim 6, wherein the lightsource is an LED.
 8. The illumination apparatus of claim 6, wherein thelight source has a lambertian angular distribution.
 9. The illuminationapparatus of claim 6, wherein the optic is circular.
 10. Theillumination apparatus of claim 6, wherein the optic is toroidal. 11.The illumination apparatus of claim 6, wherein a cross-section of theoptic, taken in a plane containing the axis about which the optic issymmetrical, has a gap, a top of the gap being in a plane of the planarexit face.
 12. The illumination apparatus of claim 11, wherein the gapis bounded by reflective walls in the optic to aid in redirection of aportion of the light from the input surface to the planar exit surface.13. An optical apparatus comprising: an optic having a planar exitsurface and an input surface, the optic being symmetrical about acentral axis of the optic; a light transmitting medium haying a firstsurface portion and a second surface portion directly opposite the firstsurface portion; and at least one coupling material adjacent to theplanar exit surface and having a refractive index greater than air, theat least one coupling material optically coupling and physicallyconnecting the planar exit surface to the light transmitting medium; theinput surface being subdivided into one or more regions or zones, eachregion or zone having a constant or smoothly changing surface tangent,and each region or zone being bounded by at least one discontinuity inthe surface tangent so that, when a light source is positioned to besurrounded by the optic and is optically coupled to the lighttransmitting medium by the planar exit surface and the at least onecoupling material, the optic redirects a first amount of the light fromthe light source, that passes through the input surface, through thefirst surface portion, and into the light transmitting medium, within arange of angles between a critical angle of the second surface portionand a complementary angle to the critical angle, and redirects most orall of a remaining amount of the light from the light source, thatpasses through the input surface, through the first surface portion, andinto the light transmitting medium, at angles greater than thecomplementary angle.
 14. The optical apparatus of claim 13, wherein thelight transmitting medium is a window.
 15. The optical apparatus ofclaim 13, wherein the optic is circular.
 16. The optical apparatus ofclaim 13, wherein the optic is toroidal.
 17. The optical apparatus ofclaim 13, wherein a cross-section of the optic, taken in a planecontaining the axis about which the optic is symmetrical, has a gap, atop of the gap being in a plane of the planar exit face.
 18. The opticalapparatus of claim 17, wherein the gap is bounded by reflective walls inthe optic to aid in redirection of a portion of the light from the inputsurface to the planar exit surface.